Three-phase generator having increased output

ABSTRACT

A three-phase generator that has a plurality of stator windings, a rectifier system connected with the stator windings, an exciter winding, a generator controller, and an additional circuit that effects an increase in voltage. This additional circuit is a passively operated booster circuit that is integrated into the generator and that has no controlled components.

BACKGROUND INFORMATION

In known claw-pole generators, the energy for the excitation is takenfrom the electrical system of the respective motor vehicle. This takesplace using a generator controller that has a switched semiconductor asa switching element. The generator controller sets the excitationvoltage between 0 V and the electrical system voltage. This is shown inFIG. 1, which depicts a diagram illustrating the positioning ofgenerator controller R between electrical system BN and excitationwinding WE of the generator.

FIG. 2 shows a known generator circuit having a generator controller R,an excitation winding WE, a rectifier system G and three stator windingsWS. The stator windings form a star connection, and are offset by 120°from one another with respect to the rotor (not shown). The beginningsof the windings, which are connected to the rectifier system, aredesignated with the letters U, V, W. When the rotor is turned, analternating voltage is produced in each of these stator windings. Thethree alternating voltages produced are offset from one another by 120°.

From German Published Patent Application No. 196 34 096, a voltagesupply system is known that has an increased output power, produced whenan increased power requirement is signaled by an external controlsignal. The known system has a three-phase generator whose windingssupply the voltage for a vehicle electrical system via rectifiers. Inaddition, the generator contains an exciter winding through which theexcitation voltage, which can be influenced by a voltage controller,flows. The exciter winding can be operated with a voltage that is higherthan the supply voltage during times that can be predetermined. Thisincreased voltage is produced through the activation of additionalwindings having rectifiers in the generator, or by a direct-currentconverter allocated to the generator. In this way, the controlling ofthe generator takes place through the voltage controller, which hascontrolled transistors, in such a way that the output voltage of thegenerator remains at the level of the electrical system.

SUMMARY OF THE INVENTION

In contrast, the present invention achieves an increased output power ofthe generator by using, as an improved magnetic utilization of thegenerator, the ripple at the exciter winding ends in order to achieve acapacitive voltage increase. This takes place economically through theuse of a passive additional circuit that has no transistors. Incomparison with circuit topologies that, for example, use direct-currentconverters for voltage multiplication, this results in advantages withrespect to the electromagnetic compatibility.

In comparison to all actively controlled additional circuits, advantagesresult the fact that no actively controlled components are required.Conventional diodes and capacitors can be used. In addition, nosaturation effects occur. The additional circuit according to thepresent invention is secure against short-circuiting and againstopen-circuit operation.

An additional voltage increase can advantageously be achieved throughthe use of a cascade connection.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an arrangement including a generator controller.

FIG. 2 shows a generator circuit provided with a generator controller.

FIG. 3 shows a drawing illustrating the arrangement of the additionalcircuit according to a first exemplary embodiment of the presentinvention.

FIG. 4 shows a drawing illustrating the arrangement of the additionalcircuit according to a second exemplary embodiment of the presentinvention.

FIG. 5 shows an exemplary embodiment of an additional circuit accordingto the present invention.

FIG. 6 shows a first exemplary embodiment of a generator circuitaccording to the present invention.

FIG. 7 shows a second exemplary embodiment of a generator circuitaccording to the present invention.

FIG. 8 shows a diagram illustrating the voltage curves at the windingtaps of the stator windings.

DETAILED DESCRIPTION

According to the present invention, an additional circuit that uses onlypassive components is inserted into a three-phase generator, preferablya claw-pole generator, and through the use of said circuit an increaseis achieved in the excitation voltage drop at the excitation winding ofthe generator. In this way, the excitation current flowing through theexcitation winding, and thus the output power provided by the generator,are also increased.

With an additional circuit according to the present invention, theoutput voltage of the generator can for example be doubled or tripled. Afurther increase of the output voltage of the generator is possiblethrough the additional use of a cascade connection.

FIG. 3 shows a drawing illustrating the arrangement of an additionalcircuit according to a first exemplary embodiment of the presentinvention. In this first exemplary embodiment, one terminal ofadditional circuit ZS1 is connected with the 14V electrical system, anda second terminal is connected, via generator controller R, to theterminal away from ground of excitation winding WE. The other terminalof excitation winding WE is connected directly to ground GND. Inaddition, additional circuit ZS1 has terminals U, V, W, that areconnected to the stator windings.

FIG. 4 shows a drawing illustrating the arrangement of an additionalcircuit according to a second exemplary embodiment of the presentinvention. In the second exemplary embodiment, a terminal of additionalcircuit ZS2 is connected to the 14V electrical system, and a secondterminal is connected, via generator controller R, to the terminal awayfrom ground of excitation winding WE. In addition, additional circuitZS2 also extends to the connection between the terminal adjacent toground of excitation winding WE and ground GND. In addition, additionalcircuit ZS2 has terminals U, V, W that are connected to the statorwindings.

FIG. 5 shows an exemplary embodiment of an additional circuit ZS1 thatcan be used in combination with FIG. 3. This additional circuit is apassively operated booster circuit situated between the 14V terminal andgenerator controller R according to FIG. 3. This booster circuit has aparallel circuit of three signal branches, each signal branch containingtwo diodes connected in series. The connection point between the twodiodes of the first signal branch can be connected with terminal U via acapacitor. The connection point between the two diodes of the secondsignal branch can be connected with terminal V via a capacitor. Theconnection point between the two diodes of the third signal branch canbe connected with terminal W via a capacitor.

In alternative exemplary embodiments, not shown in the drawing, theadditional circuit has only one parallel circuit having two signalbranches, or simply has only one signal branch, each of these signalbranches being constructed in the same way as one of the signal branchesshown in FIG. 5.

If a booster circuit according to FIG. 5 is used in a claw-polegenerator, there results the device shown in FIG. 6, which shows a firstexemplary embodiment of a generator circuit according to the presentinvention.

In addition, if such a booster circuit is additionally placed into theconnection branch between the terminal adjacent to ground of excitationwinding WE and ground, there results the device shown in FIG. 7, whichshows a second exemplary embodiment of a generator circuit according tothe present invention. This exemplary embodiment is based on theschematic design according to FIG. 4.

The curve of the winding voltages at taps U, V, W is shown in FIG. 8 forone of these winding phases. In this Figure, time is plotted on theabscissa and voltage is plotted on the ordinate. It can be seen that thewinding voltages run in approximately rectangular fashion.

In the following, the functioning of the voltage increase circuit in theexemplary embodiment according to FIG. 6 is explained in more detail onthe basis of one phase of the three-phase generator. First, a voltage of−0.7 V is present at tap U. This is because this tap U is connected withground GND via a diode, this diode having a forward voltage of 0.7 V.

A voltage of 14V is present at the capacitor situated in the U phase,said capacitor being connected to the electrical system via a diode ofthe additional circuit. A flow of current takes place from theelectrical system to the capacitor via the diode. In this way, thepotential at tap U increases to a value that corresponds to the sum ofthe electrical system voltage and the forward voltage of the diode,i.e., to a value (U_(BN)÷0.7 V). This corresponds to an increase in thecharge of the capacitor.

Subsequently, charge flows from the capacitor into the exciter circuitvia the second diode of the additional circuit. In this way, thepotential at tap U sinks again to −0.7 V. This process, which isconstantly repeated, takes place in each of phases U, V, W, with a timeoffset of 120°.

For example, let exciter current I_(err)=8A and let exciter voltageU_(err)=24V. The energy output of the capacitor is then calculated as$E = {\frac{1}{2}{C\left\lbrack {\left( {2 \cdot U_{14}} \right)^{2} - \left( {U_{err} - U_{14}} \right)^{2}} \right\rbrack}}$

For the power of the booster circuit, the following holds:$P = {f_{e1} \cdot \frac{3}{2} \cdot {C\left\lbrack {\left( {2 \cdot U_{14}} \right)^{2} - \left( {U_{err} - U_{14}} \right)^{2}} \right\rbrack}}$

In this way, the following is obtained:C≈1500 μF, if f=180 Hz.

If the boundary conditions change, different values will result.

1-5. (Canceled)
 6. A three-phase generator, comprising: a plurality ofstator windings; a rectifier system connected to the stator windings; anexciter winding; a generator controller; and an additional circuit thateffects an increase in voltage, wherein: the additional circuit includesa passively operated booster circuit that is integrated into thegenerator and that has no controlled components.
 7. The three-phasegenerator as recited in claim 6, wherein: the additional circuitincludes only diodes and capacitors.
 8. The three-phase generator asrecited in claim 6, wherein: the additional circuit has one, two, orthree signal branches, each signal branch containing two diodesconnected in series, and each connection point between the two diodesbeing connected, via a capacitor, with one of the stator windings. 9.The three-phase generator as recited in claim 6, wherein: the additionalcircuit is connected between a vehicle electrical system and a terminalaway from ground of the exciter winding.
 10. The three-phase generatoras recited in claim 6, wherein: the additional circuit includes twoparallel circuits, each parallel circuit includes three signal branches,each signal branch includes two diodes connected in series, eachconnection point between the two diodes is connected with one of thestator windings via a capacitor, one of the parallel circuits isconnected between a vehicle electrical system and a terminal away fromground of the exciter winding, and another one of the parallel circuitsis connected between a terminal adjacent to ground of the exciterwinding and ground.